Industrial lasers are used for a wide range of applications including cutting, welding, micro-machining, additive manufacturing, and drilling. No matter the application, industrial laser systems generate a significant amount of heat. There are several different types of industrial laser technologies ultimately distinguished by the power density of the laser and its use. The commonality of every laser system is the need for advanced cooling of the power source and the laser optics. The temperature stability of these components is critical to ensuring the performance of the laser system. Chillers have been used to cool industrial laser systems for decades. However, new industry refrigerant restrictions and performance requirements have led industrial laser manufacturers to demand a more eco-friendly, efficient, and maintenance-free chiller solution.
Application Overview
Efficiently cooling lasers can be a significant challenge. For example, fiber lasers have better cooling characteristics over other media due to their specific arrangement, which enables them to spread the heat over a larger surface area. Ion lasers are characterized by the generation of extreme heat during lasing and the need for elaborate cooling measures. Carbon dioxide (CO2) lasers emit heat energy in the far-infrared and microwave region of the spectrum. To ensure proper, long-term performance of the laser, heat needs to be quickly and effectively dissipated by the cooling system.
Depending on system size and configuration, waste heat may be transferred by a coolant or directly to air. For laser systems that generate heat in excess of a few hundred watts, a liquid coolant solution is warranted. Coolant is circulated through a chiller or heat transfer system to pump heat away from sensitive laser components and maintain a constant operating temperature.
Some coolant solutions feature cooling system pumps with greater pulsation. Pulsating pumps still offer the required system cooling, but create a vibration within the cooling system. In laser systems, this has similar effects to thermal instability and results in a less focused laser beam and lower quality performance, which is critical in cutting and engraving applications commonly used for cutting hard materials like steel. Basically, the laser beam melts through whatever material it is focused on. When cooled efficiently, the laser beam creates a finer, more precise cut or engraving. If the laser beam operates outside the optimum temperature range, it is not as focused and creates a rougher, less precise cut or engraving.
Application Challenges
Many challenges exist in terms of the design, implementation, and maintenance of liquid cooling systems for industrial laser systems. If an industrial laser system goes down, it can shut down the entire manufacturing processes. This can significantly impact production and incur large manufacturing costs. Therefore, robustness and maintenance-free operation of the chiller cooling system is critical to ensure maximum system uptime.
As previously mentioned, temperature stability is vital for both the industrial laser power supply and laser optics. Depending on the type of laser system and application, the heat generated from the laser can be far more than kilowatts. For optimal performance, the laser optics typically require a stable operating temperature of 20°C ± 0.1°C, while the ambient temperature may fluctuate between 23°C to 35°C in a room temperature environment.
Miniaturization of industrial laser systems has led OEMs to pack more electronics into a smaller footprint. This increases the heat flux density and adds thermal load to the unit, making the industrial laser cooling solution even more important to the efficiency and performance of the laser power source and optics. To meet the required cooling capacity in a more compact form factor, the thermal management solution must have a high coefficient of performance (COP) for cooling well below ambient temperatures. Waste heat must be managed and dissipated efficiently in order to increase laser performance while reducing power consumption and providing quieter operation (both lower noise and vibration).
Loud, vibrating machines can create an unpleasant and dangerous environment. Equipment cooling units can play a significant role in the decibel level on a manufacturing floor. New industrial laser systems require quiet operating thermal management solutions. Noise is also a consideration for the laser system in need of a retrofitted chilling unit.
Many governments are requiring OEMs to phase out the use of traditional ozone-depleting and high global warming refrigerants. Older compressor-based systems utilize environmentally harmful HFC refrigerants including R134a and R404A. Modern compressor-based systems now use a variety of natural refrigerants: R744 (carbon dioxide), R717 (ammonia), R290 (propane), R600a (Iso-Butane), and R1270 (propylene). Although they have their own complications, including flammability, these natural refrigerants are significantly better for the environment.
Comparing Cooling Technologies
Traditionally used in industrial laser applications, compressor-based refrigeration systems offer a high coefficient of performance (COP). For example, if they are cooling a heat load of 3 kW, a standard compressor-based refrigeration system typically requires around 1 kW of energy to provide the proper cooling, which is more efficient compared to thermoelectric cooling.
Compressor-based systems also tend to be smaller than alternative technologies like liquid-to-air heat exchangers, because they require less energy. Thermoelectric devices on the other hand are smaller, but they are less efficient. In addition, liquid-to-air heat exchangers do not cool below ambient temperatures like compressor-based and thermoelectric systems.
Central facility cooling systems used to cool the entire building have also been used for cooling industrial laser applications. However, these systems cannot guarantee a constant temperature and flow rate. It can also be difficult to satisfy all of the industrial cooling requirements with one large centrally controlled system.
Recirculating Chiller Solutions
Modern recirculating chillers can offer reliable and precise temperature control for industrial laser applications. Utilizing high-performance variable-speed motors, new recirculating chiller technologies offer lower noise operation and reduced energy consumption by up to 50% compared to conventional compressor-based systems.
By using environmentally-friendly refrigerant, like R513A, recirculating chillers deliver similar performance with half the Global Warming Potential (GWP) compared to traditional hydrofluorocarbons (HFC) refrigerants.
When it comes to temperature stability, recirculating chillers can achieve an accuracy of up to ±0.1°C because they have the ability to heat and cool fluid to maintain the thermal set point. Industrial laser systems benefit greatly from the precise temperature control, ensuring optimum performance of the power source and laser optics.
Innovative chillers, like the Nextreme Recirculating Chiller Platform from Laird Thermal Systems, feature an LCD touchscreen display to simplify the user interface during installation/set-up and operation. Advanced interfaces allow the user to easily control temperature setpoints, coolant type, flow and alarm settings, while the coolant level is easily monitored via the indicator window on the front panel.
With no moving parts, an optical fluid level sensor offers improved reliability and increased uptime when compared to chillers that use mechanical float switches. The programmable alarm alerts the user when the fluid level falls below acceptable operating conditions. To prevent damage to equipment in high pressure operating conditions, the chiller senses the supply fluid pressure and will alert users when low- or high-pressure limits have been exceeded. For maximum uptime, chillers can use an optional “hot-swappable” 5-micron water filter for filtering particulates from the coolant circuit, which means that there is no need to shut down the unit during maintenance.
In addition, some laser applications require deionized water in the recirculating fluid loop. To meet this requirement, the chillers can be equipped with high purity plumbing, stainless steel and plastic wetted materials suitable for operation at fluid resistivity levels of 1 to 3 MOhm*cm.
Conclusion
Properly cooling industrial laser systems is challenging, as power densities continue to increase while form factor requirements continue to shrink. However, today’s compressors are more efficient than a decade ago. Compact chiller systems offer a higher coefficient of performance that delivers efficient, low power consumption to maximize uptime and optimize performance in industrial laser systems. Innovative chillers offer quiet operation in a smaller and lighter package compared to previous versions. Recirculating chillers provide higher efficiency and reliability than air-based heat exchangers and thermoelectric devices. This enables a more focused and improved laser performance for more precise cutting, welding, micro-machining, drilling, and more.
